EC20 Sleep Mode

Wakeup pin is getting 1.8V supply

If so I am afraid you have to login in the EC20 to find out why it cannot goto suspend state.

Hello… Could u plz tell me process of login into EC20
using Debug UART

Please take a photo of the modem.

Sir, I need step by step guide of Logging into EC20 using stm32 board.

You need a TTL USB uart to login in the modem.

It has nothing to do with STM32. You can connect the EC20 with the PC via UART.